China’s “dynamic zero-Covid” policy was born out of the effort to control the initial outbreak in the city of Wuhan. People who have the virus are isolated or sent to hospitals, depending on the severity of their cases. Anyone deemed a close contact, which can be very broadly defined, is also isolated.

When outbreaks are deemed severe enough, entire cities can be shut down, as Shanghai was for almost two months this spring. The southwestern city of Chengdu, with 21 million people, is now under lockdown, and many more people around the country are under some form of restriction.

Nearly empty roads in Chengdu, China, last week after a lockdown went into effect.

Travel into China remains highly limited, although the quarantine period for those arriving from overseas has been halved to seven days followed by three days’ home isolation. The use of a contact-tracing app is required to enter public places. It issues health codes in the style of a traffic light, so crossing paths with an infected person or visiting an area deemed high risk can make someone’s health code turn from “green,” or safe, to “yellow,” potentially requiring quarantine and extensive testing. In some places regular Covid testing is required, regardless of potential exposure.